4x4 doesn't engage
 

Not sure what the problem is but I pull back on the lever and nothing happens. Thought it might be a vacuum leak cuz I might have a leaky plenum as well...but honestly I'm getting really mad at this truck and I have a feeling that this might be a big $ fix.

any ideas?

I suppose it's possible you don't have enough vacuum to engage the CAD. What's your vacuum at idle? Does the 4WD light come on?

4wd light does not come on and I haven't gotten a chance to check the vacuum yet it idles a little rough, no pinging, and I don't see any white smoke besides condensation although I could be mistaken.

so....my lovely 2wd 4x4 truck can't get out of my driveway today...why? cuz it snowed and 2wd es muy mal in the snow....I couldn't go ANYWHERE...so yeah, a little more help would be nice cuz I'm gonna need 4wd to get around now

crawl underneath your truck and at the front of the transmission (towards the front of your truck) right in front of a frame bar there is two metal lines bracketed to the brace. There should be teo lines connected to it one red and one black. Both of those should fit over the metal lines fastened to the brace. If both of them are unplugged the red line attaches to the shorter metal line and the black connects to the longer one.

If you have problems with those lines comming undone you can zip-tie them on
A leaky plenum should not loose that much vaccum to not allow your 4X4 to engage
Hope this helps

I found a chunk taken out of the bottom metal line in mine shortly after I bought it. In my case it didn't want to disengage the axle-- it would take miles before it did. I cut out that part with a dremel (about 1") and patched it with heavy vacuum tubing. Problem solved.

Another issue I had was the vacuum switch on the xfer case was stuck and the axle wouldn't disengage. This is the opposite of your issue though, and considering that it gets stuck in (don't think it could get stuck out) my opinion is that's not the problem. You could take it out and clean it anyway, it's free and easy. Just take it out with a 27mm deep socket or wrench, clean it with a mild solvent that's safe for plastic/rubber, and reinstall. It's on top of the xfer case, and has a plug with 4 vacuum lines coming out of it. Be careful not to break off any of the plastic nipples.